When you configure Azure App Service with a custom domain name, you can pick between an SNI-SSL binding type and an IP-SSL binding type. When we released the option to select your TLS version, an edge-case breaking change was also identified: sites that have SNI-SSL selected will not be able to work with TLS 1.0 selected, if receiving traffic from older browser versions.
For more information about the issue and how to resolve it, see the blog post.